A sensor is a device that detects a specific physical quantity belonging to the sensor environment, through the means of one or more detection mechanisms which converts the physical quantity to a sensor specific output signal. Well known examples of often used sensors include thermometers, speedometers, microphones, voltmeters, radars and seismometers. A subset of the general sensor concept is the mechanical sensors which detects a property of classical mechanics, e.g. acceleration, pressure and strain, and should be distinguished from sensors used for e.g. biological, medical and chemical sensing. The vast majority of modern mechanical sensors are made using microelectromechanical system (MEMS) technology, as MEMS allows for small scale sensors and inexpensive mass production. With the development of MEMS technology and the advent of micro optical sensing technologies the expanded term microoptoelectromechanical systems (MOEMS) has become widely accepted. MOEMS allows for much more versatile sensor designs and detection of quantities in more difficult accessible environments than previous technologies.
All-optical sensors have a number of advantages that make them interesting for a broader range of applications, such as the low transmission loss in optical fibers which enables remote sensing. However, compared to the vast number of electrical and opto-electrical sensors available today, all-optical sensors currently represent a small niche, since most all-optical sensors cannot in general compete with their electrical counterparts when it comes to sensitivity, dynamic range or price.
The dominating all-optical frequency modulated (FM)-based sensor today is the fiber Bragg grating (FBG) sensor where the deformation of a Bragg grating is used for modulating the signal. While FBGs have successfully been used for a number of applications they have several drawbacks, including the large physical size, low sensitivity, strict limitations on materials choice and component structuring as well as mass production shortcomings. The inventors have previously presented a novel highly sensitive all-optical pressure sensor for an audio microphone fabricated using MEMS technology. The sensing mechanism is based on modifying the effective refractive index of a hollow core anti-resonant reflecting optical waveguide (ARROW) incorporating a Bragg grating. By modifying the effective refractive index instead of the grating period a highly improved sensitivity is obtained. Sensitivities can be up to several magnitudes larger than in FBGs and comparable MEMS technology.